Research has recently focused on developing viable alternatives to combustion engines. Their increased efficiency and decreased generation of pollutants make fuel cells a particularly attractive alternative. Fuel cells generate electricity through an electrochemical reaction of fuel with oxygen. The fuel used may vary, but can be any of hydrogen, methanol, ethanol, methane, butane, gasoline, diesel, etc. The oxygen needed for the reaction is normally obtained from air.
There are several types of fuel cells, each primarily identified by the electrolyte membrane used. The most common fuel cells are alkaline fuel cells (AFCs), phosphoric acid fuel cells (PAFCs), polymer electrolyte membrane fuel cells (PEMFCs), molten carbonate fuel cells (MCFCs), and solid oxide fuel cells (SOFCs). Each of these fuel cells has unique capabilities and limitations.
A new class of fuel cells has recently been developed. These fuel cells are known as solid acid fuel cells (SAFCs) and utilize a superprotonic solid acid electrolyte such as CsH2PO4 (cesium dihydrogen phosphate or CDP) to conduct protons. These solid acid electrolytes and solid acid fuel cells are described in U.S. Pat. No. 6,468,684, entitled PROTON CONDUCTING MEMBRANE USING A SOLID ACID, the entire contents of which are incorporated herein by reference, in co-pending U.S. patent application Ser. No. 10/139,043, entitled PROTON CONDUCTING MEMBRANE USING A SOLID ACID, the entire contents of which are also incorporated by reference and in co-pending U.S. patent application Ser. No. 11/095,464, entitled DIRECT ALCOHOL FUEL CELLS USING SOLID ACID ELECTROLYTES, the entire contents of which are also incorporated herein by reference.
SAFCs have many advantages. Among these advantages are the ability to operate at intermediate temperatures, i.e. about 150 to about 350° C. Operation at these temperatures enables use of less expensive catalysts and ancillary component materials. Also, the solid acids are used in their solid state, enabling the design of simple and robust fuel cell systems. These advantages make SAFCs an economically attractive alternative to other known fuel cell types.
A typical fuel cell membrane electrode assembly (MEA) comprises an electrolyte membrane sandwiched between anode and cathode electrocatalyst layers and electrode gas diffusion layers, as shown in FIG. 1. SAFCs also utilize this MEA construction. The superprotonic solid acid electrolyte membranes distinguish SAFCs from other fuel cells.